The present invention generally relates to a fastening device and more particularly, to a buckle arrangement for a seat belt for use in a motor vehicle and the like which is adapted to be locked, with a tongue portion of the seal belt inserted in a frame of the buckle.
Conventionally, in the buckles for seat belts of the above described type, there has been proposed an arrangement in which an engaging opening is formed in one end of a tongue portion connected to the seat belt, while a retaining opening is defined in a predetermined portion of a frame of the buckle, for example, by press work so that, upon insertion of the tongue portion into the frame, a locking member provided on the frame is displaced to a position for simultaneously extending through the engaging opening of the tongue portion and the retaining opening of the frame so as to effect locking of the tongue portion.
In the known arrangement as described above, when a force is applied in a direction to withdraw the tongue portion under the locked state, the peripheral edge of the engaging opening of the tongue portion contacts the locking member, with simultaneous engagement of the locking member with the peripheral edge of the retaining opening for preventing the tongue portion from coming out. Accordingly, there has been such a problem that, when it is attempted unlock the tongue portion under the state where the tongue portion is subjected to a force in the direction of withdrawal thereof, the releasing is not readily effected due to frictional resistance between the locking member and the peripheral edge of the retaining opening. Moreover, since the engaging opening is formed by blanking of a sheet material, the peripheral edge thereof is generally rough with an increased frictional resistance, thus requiring a large force to effect the unlocking.